Some prepositions are abbreviated when combined with an article, as in the following:

in + dem = im an + dem = am

Sometimes you will hear other shortened versions of prepositions + articles, but they are not always used.

Verbs describing a position

The verbs liegen, stehen and sitzen describe a spatial area and nearly always require further explanation to answer the question Wo ...? This is why these verbs are often used with a two-case preposition that takes the dative.